[PATCH] arm64: enable THP_SWAP for arm64

[Barry Song]

From: Barry Song <v-songbaohua@xxxxxxxx>

THP_SWAP has been proved to improve the swap throughput significantly
on x86_64 according to commit bd4c82c22c367e ("mm, THP, swap: delay
splitting THP after swapped out").
As long as arm64 uses 4K page size, it is quite similar with x86_64
by having 2MB PMD THP. So we are going to get similar improvement.
For other page sizes such as 16KB and 64KB, PMD might be too large.
Negative side effects such as IO latency might be a problem. Thus,
we can only safely enable the counterpart of X86_64.

Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Shaohua Li <shli@xxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
---
 arch/arm64/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index d550f5acfaf3..8e3771c56fbf 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -98,6 +98,7 @@ config ARM64
 	select ARCH_WANT_HUGE_PMD_SHARE if ARM64_4K_PAGES || (ARM64_16K_PAGES && !ARM64_VA_BITS_36)
 	select ARCH_WANT_LD_ORPHAN_WARN
 	select ARCH_WANTS_NO_INSTR
+	select ARCH_WANTS_THP_SWAP if ARM64_4K_PAGES
 	select ARCH_HAS_UBSAN_SANITIZE_ALL
 	select ARM_AMBA
 	select ARM_ARCH_TIMER
-- 
2.25.1